Son of John Westrup, Sr., and Catalina Andres Westrup, Thomas arrived with his family in Veracruz, Mexico, in May 1852. His father, an engineer, had a contract to build a flour mill on the estate of Vicente Díaz Gollano in San Miguel de Allende.

Thomas participated in the foundation of the first evangelical church in Latin America, in Monterrey, Mexico, in 1864, and in 1867, became an agent of the American Bible Society. In 1876, he traveled to New York, where the Baptist Home Mission Society commissioned him as a missionary to Mexico. His works include: